1. Field of the Invention
This invention relates to a boat hull, in particular to hydroplaning hulls for high-speed motorboats.
2. Description of the Related Art
Ever since man first ventured onto the water in boats, he has tried to design hulls that increase speed without unduly sacrificing stability. This is of course, by definition, the main goal of designers of motor-powered speed boats, for which an increase in knots per horsepower is usually more important than an increase in load-carrying capacity.
One obvious way to increase speed is simply to increase engine power. There are several disadvantages to this solution, however. First, more powerful engines are generally heavier, which means that even more mass must be moved. Second, increased engine mass usually requires a redesign of the hull in order to provide for optimum balance under way, especially in the case of outboard engines. Third, more powerful engines also usually cost more and have greater fuel consumption than smaller powerplants.
In addition to inertia, two primary forces work against increased speed for boats, namely, the resistance of the air (aerodynamic drag) against the above-water structure of the boat and the resistance of the water (hydrodynamic drag) on the wetted surface of the hull. Many solutions have been proposed for reducing both forms of drag.
Hydrodynamic drag can be reduced not only by better streamlining the hull to minimize areas of turbulence and thus wasted energy, but also by reducing the wetted surface area of the hull. As is well known, one way to reduce the wetted area is for the hull to act as a hydroplane, such that the hull rises out of the water when at cruising speed. One way to enable hydroplaning is to mount hydrofoils on the hull, either near the bow, or both bow and aft. This of course adds structural complexity and greatly reduces the efficiency of the boat at non-hydroplaning speed.
It is also possible configure the hull itself with a step that acts as a planing surface. Examples of such stepped hulls are disclosed in the following references:
U.S. Pat. No. 4,655,157 (Sapp, Apr. 7, 1987);
U.S. Pat. No. 4,231,314 (Peters, Nov. 4, 1980);
U.S. Pat. No. 4,027,613 (Wollard, Jun. 7, 1977); and
U.S. Pat. No. 5,191,853 (Adler, Mar. 9, 1993).
One problem with stepped hulls is that they often create under-pressurexe2x80x94a vacuumxe2x80x94behind the steps. This vacuum tends to xe2x80x9csuckxe2x80x9d the hull down, thereby increasing drag and reducing efficiency. One common way to overcome this problem is to build channels into the hull, for example, perpendicular to or along the strakes, that direct air into the region(s) behind the step(s) to compensate for any vacuum effect. These hulls are commonly referred to as xe2x80x9cventilatedxe2x80x9d or xe2x80x9caeratedxe2x80x9d hulls.
What is neededxe2x80x94and always sought afterxe2x80x94is a boat hull that allows for even greater speed for a given motor effect, or that achieves a given speed with less motor effect, compared with existing hulls. This invention provides such a boat hull.
The invention provides a hydroplaning boat hull that has: a forward portion; an aft portion; at least one midship step separating the forward and aft portions; a forward planing surface that extends transversely immediately forward of the midship step and has a forward angle of attack; and an aft planing surface portion that extends transversely and forward of an aft edge of the hull and has an aft angle of attack. The forward angle of attack lies in the range 2.0-6.5 degrees, and when the hull is moving at least at a minimum planing speed, the forward and aft planing surfaces constitute two separated wetted surfaces.
In the preferred embodiment of the invention, the forward and aft angles of attack are equal. Moreover, at least the forward angle of attack is preferably 5.5 degrees when the deadrise D of the hull is 18 degrees; the deadrise itself is preferably at least 16 degrees. At least the forward angle of attack is preferably related to the deadrise as follows: Given a reference angle of attack of 5.5 degrees, for every degree by which D exceeds 18 degrees, the forward angle of attack is preferably increased by an increment A above the reference angle of attack, and for every degree by which D is less than 18 degrees, the forward angle of attack is preferably decreased by the increment A below the reference angle of attack. The optimum value for A has been found to be 0.1 degrees.
The longitudinal location of the midship step also affects performance. In the preferred embodiment of the invention, given a projected chine length L, the midship step is preferably located longitudinally in a range of 0.45 to 0.51 times L, measured aftward from a forwardmost point of the chine; the optimum position of the step has been found to lie a position 0.48 times L, again measured aftward from the forwardmost point of the chine.
Both the aft and forward portions are preferably twisted, each with a deadrise angle at the keel line that increases from a respective leading edge forward.
The preferred embodiment of the hull is unventilated.